The embodiments described herein relate generally to a flow control system for use with a wind turbine and, more particularly, to a flow control system having an aperture control system.
Active flow control (AFC) is a general term for technologies and/or systems that actively attempt to influence an aerodynamic response of an object in reaction to given in-flow conditions. More specifically, at least some known AFC systems are used to manipulate flow conditions across an airfoil. As used herein, the term “airfoil” refers to a turbine blade, a wing, and/or any other suitable airfoil. Although the embodiments described herein refer to a turbine blade, it should be understood that the embodiments described herein may be used with any suitable airfoil. In contrast to known passive flow control systems that provide substantially constant flow control, known AFC systems enable flow control to be selectively applied to an airfoil.
At least some known AFC systems use air distribution systems to manipulate a boundary layer of air flowing across a surface of an airfoil. For example, AFC systems discharge air into the boundary layer to reduce skin friction between a flow across the blade and a surface of the blade. Known AFC systems include actuators that can be divided in two categories, depending on their net-mass-flow. The first category is zero-net-mass-flow actuators, such as synthetic jet actuators, and the second category is nonzero-net-mass-flow actuators, such as air ejection actuators, which may be steady or unsteady and/or blowing and/or suction actuators.
Some known AFC systems can cause boundary layer blow-off by discharging air with such force that the AFC air flow blows through the boundary layer and creates drag at the point of discharge. Such discharged air generally does not return into a near wall region to provide skin friction reduction until far downstream from the discharge point. As such, a relatively large amount of air is required to be discharged from the AFC system because a relatively large fraction of the AFC air flow does not flow along the near wall region to reduce skin friction.
Further, when at least some known AFC systems are deactivated such that no AFC air flow is discharged from the AFC system, debris and/or insects can enter the AFC system and foul an air distribution system of the AFC system. Moreover, wind gusts suddenly increase an effective angle of attack of the blade, which can yield high, unsteady loads on the blade. Such high and/or unsteady loads can adversely affect a structure of the blade.